1. Field of the Invention
The present invention relates to a method and an apparatus for controlling a vehicular air-conditioning system, for controlling the operation of the air-conditioning system when an engine of a vehicle such as an automobile is in a racing state, i.e., in a so-called idling state.
2. Description of the Related Art
A control apparatus for a vehicular air-conditioning system has been hitherto known (see Japanese Laid-Open Utility Model Publication No. 1-147718), which is used in order to prevent the stop of an engine, i.e., so-called engine stop during the operation of the air-conditioning system. In this conventional technique, the operation of the air-conditioning system is stopped when the actual idling number of revolution (net idling number of revolution) of the engine is below a lower limit target value of the idling number of revolution. On the other hand, the operation of the air-conditioning system is started again to use the system when the net idling number of revolution is restored to be not less than an upper limit target value of the idling number of revolution.
However, this conventional technique involves the following problem. That is, if the control is performed so that the number of revolution of the engine is lowered when a large load is exerted on the air-conditioning system and a large load is also exerted on the engine, then the rotation of the engine varies between the upper limit target value of the preset number of revolution (number of revolution to restore the air-conditioning system) and the lower limit target value of the preset number of revolution (number of revolution to stop the air-conditioning system), sometimes resulting in occurrence of hunting.
A technique to solve this problem has been suggested in Japanese Laid-Open Patent Publication No. 5-44531. This technique includes a so-called idle-up control means for increasing the idling number of revolution depending on the load exerted on an air-conditioning system when the air-conditioning system is operated. This technique includes an intake amount-correcting means for increasingly correcting the air increment amount value for the idle-up effected by the idle-up control means after the air-conditioning system is allowed to be in a stopped state at the lower limit target value. Incidentally, the idle-up control refers to the control in which the intake amount-correcting means is operated so that the amount of intake air into the engine is increased in response to the operation and the stop of the air-conditioning system during the idling state in order to idle-up the engine.
However, in the technique described in Japanese Laid-Open Patent Publication No. 5-44531, the problem described above is dealt with such that the amount of air is increasingly corrected by using the intake amount-correcting means after the air-conditioning system is in the stopped state to give no load exerted on the engine by the air-conditioning system. Therefore, the so-called boosting phenomenon tends to occur, in which the number of revolution of the engine is quickly increased depending on the air increment correction amount value and the state of the engine. For this reason, it is difficult to set the air increment correction amount value. In this technique, the control is complicated, in which the increment correction is performed, for example, in a stepwise manner. Further, any of the techniques disclosed in Japanese Laid-Open Utility Model Publication No. 1-147718 and Japanese Laid-Open Patent Publication No. 5-44531 involves the following inconvenience. That is, for example, if the number of revolution of the engine is temporarily decreased, due to any cause, to be lower than the lower limit target value in a state in which the air-conditioning system is normally operated with a small load, the air-conditioning system is stopped.
Furthermore, any of the techniques disclosed in Japanese Laid-Open Utility Model Publication No. 1-147718 and Japanese Laid-Open Patent Publication No. 5-44531 involves the following problem. That is, for example, if the decrease in number of revolution of the engine continuously occurs, in which the net idling number of revolution does not arrive at the lower limit target value of the idling number of revolution, and the engine stop does not occur, then, for example, the body of the vehicle makes vibration due to vibration of the engine, or the booming noise occurs in the vehicle's cabin due to the vibration, because the air-conditioning system is continuously operated. As a result, the evaluation of so-called sensory properties is deteriorated.